Digital projection systems can exhibit variations in gain and intensity (offset) from pixel to pixel. These variations can be due to variations in the driving electronics, the light modulator, the projection optics, the display screen, and the illumination optics. Electronic systems can be developed to correct for the variations by applying gain and offset correction values to each pixel. U.S. Pat. No. 6,061,102 issued May 9, 2000 to Sheppard et al. shows a target brightness map that is generated for each of a plurality of preselected shading application points and the target brightness map is used to correct the input signal to the display to remove variations in the display. The shading process is automatically performed during projector setup.
One problem with this approach is that the Sheppard et al. device uses a CCD sensor wherein each pixel in the sensor senses a large number of pixels in the display and is therefore unable to correct for variations in individual pixel intensity. There is a need therefore for an improved method and apparatus for correcting variations in display pixel intensity that avoids the problems noted above.